Recent display devices mostly adopt touch screen input schemes in which users perform input operations by directly touching a screen with fingers or electronic pens. Such touch screen input schemes are mainly used in portable terminals such as smart phones, cellular phones, notebook computers, all-in-one Personal Computers (PCs), tablet PCs, and Portable Multimedia Players (PMPs). In the touch screen input schemes, an intuitive and convenient user interface, instead of a keyboard, a mouse, or a physical button, can be provided as an input means for inputting position information indicated by a user by the user touching a particular position on a display screen. In particular, a touch input scheme using a pen is effective for more precise coordinate designation than a touch input scheme using a finger, and thus is suitable for a graphic task such as Computer-Aided Design (CAD).
Such a touch screen input scheme is also called a digitizer or an Electric Graphic Input Panel (EGIP), and can be classified into a resistive type, a capacitive type, an Electro Magnetic Resonance (EMR) type (or electromagnetic type) depending on a way to detect a position indicated by a user.
The resistive type senses a position pressed by a pressure in a state where a Direct Current (DC) voltage is applied, based on a change of the amount of current, in which contact between two thin conductive layers on a screen by a pressure applied by a finger or an electronic pen such as a stylus pen is sensed.
The capacitive type performs sensing by using capacitance coupling in a state where an Alternative Current (AC) voltage is applied, in which a sensing target needs to be a conductor and a contact area larger than a predetermined area is required to apply a change of a capacitance which can be sensed.
The EMR type uses a so-called digitizer sensor board having loop coil arrangement. Thus, when the user moves the electronic pen, the electronic pen is driven by an AC signal to generate a resonating magnetic field, and the resonating magnetic field induces a signal in a coil of the digitizer sensor board, such that a position of the electronic pen is detected by the signal induced in the coil.
The EMR type recognizes the position of the pen by mounting multiple coils in the board and sensing an electromagnetic change occurring by the approach of the pen. As a result, unlike in the resistive type, the sensor board is not necessarily disposed on a front side of a display module and it can also be mounted on a rear side of the display module. Thus, a multi-input device is also provided which enables an EMR-type digitizer (touch) input device and a capacitive-type touch input device for sensing a user's finger touch at the same time.
An example of a touch screen input scheme is disclosed in Korean Patent Publication No. 10-2012-0079595 filed by the present applicant, invented by Kwan-hyoung Kim and Ju-hoon Lee, published on Jul. 13, 2012, and titled “Method and Apparatus for Correcting Input Error of Input Device”.
In various portable terminals, structures for mounting a touch screen, a battery, and various circuits are disposed, and they can be causes for interruption or disturbance of a magnetic field, especially in the EMR-type touch screen. As a result, distortion of an input sensing signal through the touch screen occurs, negatively affecting the performance of the touch screen.